Turbine engine start and re-start capabilities may be designed based on a characterization performed across the ground and flight envelope and/or based on a simulation model. In some embodiments, the start and re-start processes involve two phases: direct fuel flow control and sub-idle acceleration governing. While in the sub-idle acceleration phase, a control system adjusts the fuel flow to maintain a pre-defined acceleration reference. The objective is to ensure that the proper fuel and acceleration schedules are identified to efficiently start the engine in all conditions while avoiding undesirable engine behaviour, such as compressor stall, overheating, engine hang, or flameout.
The engine start process may involve conflicting requirements. For example, cold engine acceleration requirements may be dictated by compressor stability, while hot or high speed engine restart acceleration must be high enough to prevent engine flameout. For simplicity, fuel and acceleration schedules are sometimes defined as a compromise that results in limiting the aircraft speed for engine restart or simply not achieving the shortest possible time to idle in all cases.
As such, there is room for improvement.